1. Field of the Invention
The present invention relates to a design regarding the linear roller guide unit for compressive load, which is applied in the linear transmission device and is capable of substantially improving the performance of the linear roller guide unit in many respects, including the service life, the structural strength, the rigidity, the load capacity and the impact-resistant.
2. Description of the Prior Art
The existing linear guideway essentially comprises a rail and a slide block. The rail is an elongated structure defined with rolling grooves for allowing the rollers to circulate therein. The slide block is reverse U-shaped and also defined with grooves for cooperating with the rolling grooves. And two end caps are installed at both ends of the slide block to enable the rollers to circulate. Each of the end caps is defined with a return path for enabling the rollers to circulate from the slide block to the rail.
The existing technologies for the roller type linear guideway are generally classified into the following categories:
Firstly, four-row type linear roller guide unit is one of the conventional technologies, for example, which is disclosed in U.S. Pat. Nos. 4,692,037, 4,715,729, 6,109,789 and JP Pt 60139912. FIG. 1 shows a conventional four-row linear roller guide unit, wherein the four rows of rollers are arranged at both wing portions of the slide block 22 in a crossed manner.
After analyzing the structural strength and the geometric relation, with reference to FIG. 2, it is found that the four-row type linear roller guide unit has the following disadvantages:
1. When the rail is subjected to a compressive load F, the compressive load will be applied to the lower two rows of rollers 34,35 only, and this is likely to cause trumpet deformation of the slide block 32, and a poor precision of the linear guide unit.
2. when only two rows of rollers 35 carry the compressive load, the rollers will produce a comparatively large contact stress, and as a result, the material of rollers are more susceptible to fatigue, substantially reducing the service life of the linear guide unit.
Secondly, U.S. Pat. No. 5,672,011 discloses another six-row type linear ball guide unit, as shown in FIGS. 3 and 4, wherein the six rows of balls 30 are horizontally arranged at both wing portions of the slide block 10. This design requires three circulating holes 4 to be formed in each wing portions of the slide block 101 to allow for the circulation of the balls 30.
After analyzing the structural strength and the geometric relation, with reference to FIG. 4, it is found that the six-row type linear roller guide unit has the following disadvantages:
1. The thickness of the slide block 10 will be substantially reduced under the condition that the cross section is fixed, result in a poor structural strength of the slide block, and this is likely to cause trumpet deformation of the slide block 22 and a poor precision of the linear guide unit.
2. As compared to the line-to-line contact relation between the roller and the surface of the rolling path, the balls 30 are in a point-to-point contact with the rolling path 50. When carrying the compressive load, the balls 30 will produce a comparatively large contact stress, thus accelerating the material fatigue of rollers, substantially reducing the service life of the linear guide unit.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.